Evaporators having hollow platelike vertical heat transfer elements and overhead nozzles

ABSTRACT

AN INSTALLATION FOR THE CONTINUOUS EVAPORATION OF A SOLVENT AND THE CONTINUOUS CONCENTRATION OF AT LEAST ONE SUBSTANCE IN SOLUTION IN THE SAID SOLVENT, COMPRISING A HEAT-EXCHANGER WHICH SERVES AT THE SAME TIME AS A HEATER AND AS CONCENTRATION DEVICE, THE HEAT-EXCHANGER COMPRISING A PLURALITY OF PARALLEL EXCHANGE ELEMENTS OVER WHICH A DISTRIBUTOR UNIT CAUSES THE SOLUTION TO BE TREATED TO STREAM, SAID UNIT BEING PROVIDED FOR THE PURPOSE WITH AS MANY NOZZLES AS THERE ARE EXCHANGE ELEMENTS.

F. I AURENTY 3,616,835 EVAPORATORS HAVING HOLLOW, PLATELIKE, VERTICALHEAT Nov. 2, 19H

TRANSFER ELEMENTS AND OVERHEAD NOZZLES 6 Sheets-Sheet 1 Filed Feb. ll,1969 Nov. 2, 19'71- 3,616,835 PLATELIKE, VERTICAL HEAT F. LAURENTYEVAPORATORS HAVING HOLLOW,

TRANSFER ELEMENTS AND OVERHEAD NOZZLES Filed Feb. 11, 1969 6Sheets-Sheet f3 mvenor: :Franois Lcuueniu 33: q 4.2m@ ttornegs NOV. 2,1971 F AURENTY 3,616,835

EVAPORATORS HAVING HOLLOW, PLAlELIKE, VERTICAL HEAT TRANSFER ELEMENTSAND OVERHEAD NOZZLES Filed Feb. ll, 1969 6 Sheets-Sheet .'5

FIGS

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EVAPORATORS HAVING HOLLOW, LLA'IELIKE, VERTICAL HEAT TRANSFER ELEMENTSAND OVERHEAD NOZZLIIS Filed Feb. ll, 1969 6 Sheets-Sheet Il[meezit/'aff' mvanor: ranoLe Lomnuj 35: ,Biowwz 2 20.164,

Httornes Nov. 2, 1971 F. LAUREN-ry 3,616,835

EVAPORATORS HAVING HOLLOW, PLA'lELIKE, VERTICAL HEAT TRANSFER ELEMENTSAND OVERHEAD NOZZLES Filed Feb. ll, 1969 6 Sheets-Sheet 5 H514 F/GJSF/G.76

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Wwencov: :Franois Lauvwuj Qhtomegs Nov. 2, 1971 F. LAURENTY 3,616,835

EvAPoRATORs HAVING HOLLOW, ELATELIHE, VERTICAL HEAT TRANSFER ELEMENTSAND OVERHEAD NOzzLEs Filed Feb. 11, 1969 e sheets-sheet e XXI Ze'lll'rmyw' 275 Aww/Qur 77 fIi' 272 t wd 262 265i Z Anm/aff )gaie invencor;Tra-Cols Lomvenkg 35= sgpww i 4.1m#

Qttornes United States Patent O 3,616,835 EVAPORATORS HAVING HOLLOW,PLATELIKE, VERTICAL HEAT TRANSFER ELEMENTS AND OVERHEAD NOZZLES FrancoisLaurenty, Le Touquet, France, assignor of fractional part interest toC.O.C.E.I. S.A., Paris, France Filed Feb. 11, 1969, Ser. No. 798,339Claims priority, application France, Feb. 20, 1968, 140,468; Jan. 8,1969, 6900106 Int. Cl. B01d 1/22 U.S. Cl. 159-13 B 22 Claims ABSTRACT OFTHE DISCLOSURE An installation for the continuous evaporation of asolvent and the continuous concentration of at least one substance insolution in the said solvent, comprising a heat-exchanger which servesat the same time as a heater and as a concentration device, theheat-exchanger comprising a plurality of parallel exchange elements overwhich a distributor unit causes the solution to be treated to stream,said unit being provided for that purpose with as many nozzles as thereare exchange elements.

The present invention relates to installations provided for thecontinuous evaporation of a solvent of any kind and/ or for thecontinuous concentration of at least one substance in solution in asolvent, with or without extraction of the said substance.

A conventional installation for the continuous evaporation and/orconcentration comprises generally, in a closed circuit, a circulationpump, a heater, an evaporator independent of the said heater, andconnecting pipe-work. An intake pipe introduces into this circuit theliquor to be thickened and an outlet piping system for the extraction ofthe thickened liquor. The whole assembly forms a treatment stage.

In order to economize heat, these installations most frequently comprisea number of stages in cascade. The condensed liquor in a first stagesupplies -a second stage heated by the steam formed in the first stage,and so on.

In certain installations, the condensed liquor is the end productdesired or obtained; in others, there is crystallization of one or moresubstances, and the crystals thus formed which constitute the finishedproduct desired or obtained, are extracted either in drying circuitsindividually associated with the various stages of the installation, orin a terminal drying circuit common to all the stages of theinstallation.

These installations all have numerous disadvantages.

In the first place, the heating of the liquor in the heater is notuniform; there is a formation of bubbles of vapour even inside the saidliquor. This is also true for the evaporator, especially due to thelarge thickness of liquid to which, in a conventional apparatus, isapplied the heat necessary for producing the desired evaporation. Thebubbles thus formed burst and cause the production of droplets of liquidwhich are mechanically carried away by the vapour thus liberated. Thisphenomenon, known as leading, adversely affects the efficiency of theinstallation and may result in the elimination of a not-negligiblequantity of liquor.

In addition, the existence of these bubbles causes local superheatingbetween them and the walls, which may result in a degradation of thematerials, and especially of their taste, such as caramelization.

In installations comprising a number of stages, the temperaturedifference existing between the primary and the secondary fluids issubstantial, of the order of 5 to C., both for a heater and for anevaporator, so

ICC

that the temperature loss resulting from one stage inevitably amounts to10 to 20 C.

The present invention has for its object an installation for thecontinuous evaporation of any particular solvent and for the continuousconcentration of at least one substance in solution in the said solvent,which is free from the above drawbacks and which furthermore offersother advantages.

The installation according to the invention, which comprises a heatexchanger in which circulate, on the one hand, the solution to betreated and, on the other hand, a heat-exchange fluid, is characterizedin that the said heat exchanger comprises a body, a plurality of similarexchange elements arranged in parallel at a distance from each otherinside the said body and each formed by two thin walls arranged at asmall distance from each other, a primary intake introducing the saidexchange fluid between the said Walls and a secondary intake causing thesaid solution to stream over the said walls, the said secondary intakecomprising as many outlet nozzles as there are exchange elements, andeach of the said nozzles being arranged directly above one of the saidexchange elements.

The heating of the solution and its partial evaporation are effected, inaccordance with the invenition, and contrary to the usual installations,in a single apparatus, namely the heat exchanger, which alreadyeliminates one of the causes of bubbling and therefore of overheatingand leading or priming.

In addition, by virtue of the structure of this exchanger, theintroduction of heat is effected through a very small thickness ofsolution and therefore the evaporation of the solution is also effectedwithout bubbling and therefore without priming.

Furthermore, other things being equal, this structure has the advantagesof permitting conjointly an increase in surface area of the exchangerwalls and a reduction of the thdickness of the walls and, inconsequence, a substantial reduction of the variation of temperatureintroduced by any particular stage of treatment.

It is therefore possible, in an installation of given characteristcs, toprovide the arrangement of a greater number of stages or effects andtherefore to improve the productivity of this installation.

The characteristic features and advantages of the invention willfurthermore be brought out in the description which follows below, givenby way of example reference being made to the accompanying diagrammaticdrawings, in which:

FIG. 1 is a general view with parts broken away of a crystallizationinstallation in accordance with the invention;

FIG. 2 is a view in cross-section taken along the line lI-II of FIG. 1,of an evaporator utilized in this installation;

FIG. 3 is a view in transverse section, to a larger scale, of one of theunitary elements of this evaporator;

FIG. 4 is a view in elevation with parts broken away, of a dryeremployed in the installation according to the invention;

FIG. 5 is a half-view in cross-section of this dryer, taken along theline V-V of FIG. 4;

FIG. 6 is a general View of an installation with several stages,according to the invention;

FIG. 7 is a view similar to FIG. 2 and relates to an alternative form ofconstruction;

FIG. 8 is a view in elevation of this alternative form, partlydismantled;

FIG. 9 is a view in cross-section taken along the line IX-lX of FIG. 8,of one of the elements of this alternative construction;

FIGS. 10A, 10B are partial views in cross-section, to a larger scale,taken respectively along the lines XA-XA and XB-XB of FIG. 9;

FIG. 11 is a partial view in cross-section, to a different scale, takenalong the line XI-XI of FIG. 10A;

FIG. l2 shows a crystallization diagram, given by way of example;

FIG. 13 is an elevational view similar to FIG. 8 and relates to anotheralternative form of heat exchanger in accordance with the invention;

FIG. 14 is an end view of the exchanger shown in FIG. 13, looking in thedirection of the arrow XIV of this ligure;

FIG. l is a view in transverse section of this exchanger, taken alongthe line XV-XV of FIG. 13;

FIG. 16 is a detail plan View of one of the components of thisexchanger, looking in the direction of the arrow XVI of FIG. 13;

FIG. 17 is a partial, elevational, cross-sectional view, to a largerscale, of this exchanger;

FIG. 18 is a detail View, in elevation of another alternative form ofconstruction, shown in elevation;

FIG. 19 is a detail, elevational, cross-sectional view of anotheralternative form of construction;

FIG. 20 is a view in axial section of a dryer capable of being utilizedin an installation according to the invention;

FIG. 21 is a half-view plan of this dryer taken along the line XXI-XXIof FIG. 20;

FIG. 22 is similar to FIG. 21 and concerns an alternative form ofconstruction.

In conformity with the form of embodiment chosen and shown in FIG. 1, aninstallation according to the invention, applicable for example to thecrystallization of hyposulphite, comprises an evaporation circuit and adrying circuit 11.

The evaporation circuit 10 comprises a single heat exchanger 12,described in detail below, and a centrifugal separation chamber 13 inwhich rotates a circulating pump with a wheel, helix or the like, drivenby a motor 14.

The exchanger 12 is coupled to the separation chamber 13, on the onehand by a pipe and on the other hand by a conduit 16, on which there maybe mounted, as shown, a crystallizer 17. In practice, this latter isconstituted by a simple section of diameter larger than the pipe 16, andcan also be interposed equally well in the same way on the pipe 15.

In the body of the exchanger 12 are mounted a plurality of similarexchange elements 21, arranged parallel to each other and at a smalldistance from each other.

Each element 21 is as shown in FIG. 3 composed of two thin walls 22A,22B, each having a depression zone of small depth, 23A, 23Brespectively, limited by a peripheral edge 24A, 24B respectively. Thewalls 22A, 22B are faced by their peripheral edges 24A, 24B, and theseedges are rigidly iixed in a fluid-tight manner to each other, forexample by welding.

In addition, the walls 22A, 22B are provided here and there withstiening bosses 122A, 122B respectively, supported in pairs between onewall and the other, and ixed to each other rigidly if so required.

These walls 22A, 22B may be made of metal or synthetic material. Theyform conjointly an elongated pocket of which two main coplanardimensions are substantially greater than the corresponding transversedimension.

The exchange elements 21 are arranged vertically in the body 20 and thislatter is slightly inclined to the horizontal, so that the upper edge ofeach of the elements 21 is slightly inclined to the horizontal.

`0n the upper edge of each of the elements 21 is engaged a distributorpipe 25 provided for that purpose at its lower portion with a slot 26formed along a generator line.

The pipes 25 are horizontal or inclined to the horizontal at an anglediierent from that of the body 20, so that they are engaged more andmore deeply over the upper edges of the element 21, in the direction ofthe free extremities of these latter. The pipes 25 are coupled inparallel to the conduit 16 leading from the separation chamber 13.

At its upper portion, the body 20 of the exchanger 12 is provided with acollecting cone 27 coupled by a pipe 28 to a compression vessel 29.

This compression vessel 29 is connected at its base by a pipe 30 to avacuum pump 31, which may be for example of the liquid-ring type.

The compression vessel 29 is further connected by a discharge nozzle 32to the various exchange elements 21 of the exchanger 12 by nozzles 35(FIG. 3), connected in parallel and each discharging into the upperportion of a respective one of the said elements. In the dischargenozzle 32 is engaged a pipe 37 fed with live steam and controlled by aregulating valve 38. It would of course be possible to use any othertype of steam compressor, mechanical or the like..

At its lower portion, each exchange element 21 of the exchanger 12 isconnected by a pipe 39 to the vacuum pump 31.

Furthermore, for reasons which will be explained below, pipes 33 and 34are branched to the elbows of the conduit 16.

The drying circuit 11, shown in FIG. 1, comprises a circulating pump 40,the suction of which is connected by a pipe 41 to the separation vessel`13 at the base of this latter, while the delivery side of the pumpsupplies a separation hydro-cyclone 43 through a pipe 42. The deliveryside of the pump 40 is also connected to the separation vessel 13 by areturn pipe 44 controlled by a valve 45.

In practice, the valve 45 is preferably always slightly open. Thisarrangement maintains a desirable agitation in the bottom of theseparation vessel 13. In addition, it enables part of the delivery ofthe pump 40 tol be absorbed, this delivery being in general greater thanthat of the drying circuit 11.

The hydro-cyclone sends a liquor, which is saturated but free fromcrystals, to the separation vessel '13, through a pipe y416.

The dryer 48 is shown in detail in FIGS. 4 and 5. It comprises, in knownmanner, a conical sieve 52 rotatably mounted in a chamber or tank 54.The liquor to` be dried is from hydro-cyclone 43 at 47 along the axis ofthe sieve 52 and this latter ensures the separation or sifting of thedesired crystals, which fall at 53, from a practically liquid pasteforming the drying reflux, the latter being evacuated from the chamber54 by a conduit 58. There is diagrammatically shown at 57 the Scraperswhich may be employed if so desired, in drying machines of this type.

With the sieve 52 of the drying machine are associated one or more fixedspraying racks 60, arranged in proximity to the external wall of thesieve, parallel to the generator line of this latter. This rack or racksis coupled to a supply pipe 61 through which the under-saturated dense-filtered liquor is introduced into the installation.

`On this pipe 61 is connected, as shown in FIG. 1, a branch pipe 62controlled by a valve 63 and providing a counter-flow within the conduit518 up to the point where conduit A58 opens into the chamber 54.

This conduit 58 connects the dryer 48 to the separation vessel 13 inwhich, after the junction of conduit 58 with the pipe 46, the outlet ofconduit 58 forms the intake 70 for previously established crystals, aswill be explained below; this intake 70 is preferably arranged as closeas possible to the point at which the conduit 15 opens into theseparation vessel 13, so as to take advantage of the high upward speedresulting from the large flow-rate in this latter conduit.

In addition, in the conduit 58 is interposed a fractionating means 65for crystals, which for example may be a ball grinding mill orpreferably a simple mixer of the type utilized for example for domesticpurposes. It is also possible to place any other fractionating means atany other point of the installation which contains crystals.

The operation of the installation is as follows:

The liquor contained in the evaporation circuit 1'0 carries crystals,the latter being introduced at 70` into the separation vessel 13 as willbe explained below. This liquor is kept in continuous circulation in thecircuit by the pump of the vessel 13v and, after passing into thecrystallizer 17, this liquor is distributed by the pipes 25 over theelements 21 of the exchanger 12; it constitutes the secondary fluid ofthis exchanger, the primary heating fluid of which is steam introducedinto the elements 21, as will be explained below.

As will have already been noted, and by reason of the inclination of theexchanger 12 relative to pipes 25, the cross section available for thepassage of liquid in pipes 25 is smaller at their downstreamextremities, as indicated in FIGS. l and 3, and this advantageouslycompensates for the quantity already discharged upstream of the saidextremities.

The pipes 25 should preferably be constructed in such manner as tocomply with the two following essential features:

The distribution of the liquid to be spread over the elements 21 must beas uniform as possible over each element and no crystal should becapable of blocking the slots 26, shown in FIG. 3.

In contact with the elements 21, along the walls of which it streams ina very thin film, as shown diagrammatically at 75 in FIG. 3, thedistributed liquor is subjected to a partial vaporization but, as hasbeen explained above, this vaporization is advantageously carried outwithout bubbling, and therefore without priming and without localoverheating. This vaporization results in a concentration of the liquorand, if this concentration is carried sufficiently far, causes asubsequent increase in size of the previously formed crystals which arecarried by the said liquor, as will be explained below. 'Such increase1n size may also be produced upstream and/or downstream of the heatexchanger, for example in the crvstallizer 17.

The non-vaporized liquor is taken by the conduit and returned to theseparation vessel 13.

The vapour liberated in the exchanger 12 above the treated liquid iscollected by the cone 27 and dlrected by this latter to the compressionvessel 29; then, by means of the discharge nozzle 32 and conjointly witha pressurized solvent vapour coming-in through the pipe 37, it isintroduced into the elements 2.1 of the exchanger 12, of which itconstitutes the primary fluid.

The condensed solvent vapour is removed by the pump 31.

In the separation vessel 13, the crystals are classified, or sorted, dueespecially to the rising ilow induced 1n this vessel by the pump whichit contains. At the bottorn of the vessel 13, the concentrated liquorloaded with crystals is taken by the pump 40 of the drying circuit 11and is directed by this pump to the hydro-cyclone 43.

The spent liquor can be extracted by the pipe 33 and/ or by the pipe'34, this liquor being easily separated from the large crystals by thehydro-cyclone 43 for example, by the cyclone action resulting from theconnection of these tubes in the elbows of the conduit 16, or byappropriate filtration. This spent liquor returns to the associatedpreparation unit, preferably after ltration.

The thick mass of crystals leaving the hydrocyclone 43 passes into thedrying apparatus which removes the largest crystals by sifting; thesecrystals fall at 53 and constitute in the present case the lfinalproduct.

The liquid paste which passes through the basket of the dryingapparatus, and which still contains crystals of small size, is directedthrough the conduit 58 to the separation vessel 13 of the evaporationcircuit. The crystals conveyed by this paste constitute for thiscircuit, a source of supply of pre-formed crystals.

As they pass through, these crystals are brought to the desireddimensions by the fractionating means 65. These dimensions may forexample be of the order of 1D0/i. According to the invention, the use ofcrystals split-up in this way is of particular advantage, sinceexperience has shown that such crystals generally grow faster thannaturally-formed crystals.

The fresh liquor is the concentrated 4filtered under-saturated liquorintroduced into the drying apparatus 48 by the pipes 61 and 62. Thecorresponding points of introduction of this liquor as described abovehave been chosen so as to ensure a systematic elimination of the nuclei,which without this arrangement, would have a tendency to developspontaneously in the vicinity of these points. In addition, the liquorintroduced through the pipe 62 mechanically carries away the crystalswhich would have a tendency to be decanted in the tank 54 of the dryingapparatus shown in FIG. 4.

A similar arrangement, namely the introduction of under-saturatedliquor, is preferably adopted for all the points of the installation atwhich a nucleation of this kind would have a tendency to take placespontaneously, due to the favourable heat or mechanical conditions.

As this nucleation is most frequently prolific, and as the averageindividual mass of the crystals for a given hourly production isinversely proportional to the number of nuclei formed, the crystalsobtained in the usual crystallization installations only rarely attain asubstantial size.

As will be readily understood, the controlled preferential growth ofpre-formed crystals, as Carried out in the installation according to theinvention, enables, by a judiciously arranged extraction, a productionof crystals of the desired size and in particular large crystals.

Experience has in fact shown that in a saturated liquor, the largecrystals develop at the expense of the nuclei and even of the smallcrystals, and in addition, contrary to generally accepted opinion, thespeed of crystallization increases, within certain limits, with the sizeof the crystals.

Now, as is well known for reasons of facility of water removal anddrying without dust removal, of ease of storage without setting into asolid mass and without formation of arches, of facility of handlingwithout going into lumps, of economy of transport without sticking tothe walls, together with other advantages, it is of the greatest valueto obtain crystals which are as large as possible, and this is theeconomic basis of the installation according to the invention.

lIn addition, it has been established that crystals so obtained by thegrowth of pre-formed crystals are, other conditions being equal, purerthan the crystals developed in the traditional manner from. nuclei.

The number, as large as possible, and the size of the pre-formedcrystals introduced into the treated solution, are of course chosen insuch manner that the presence of these crystals is compatible with asuitable circulation of the product in question.

In the manner described above, the fresh solution is introduced into thedrying apparatus 48.

The advantages of this arrangement will be better understood byreferring now to lFIG. l2 which is a concentration-temperature diagram,on which there has been transferred a typical solubility curve C1 of theproducts for which the solubility of the crystals increases with thetemperature-in most cases these are hydrated crystals-and a typicalsolubility curve C2 of the products for which the solubility of thecrystals diminishes with increasing temperature, and in most cases theseare anhydrous crystals. These curves intersect at D on a vertical linehaving an abscissa tD.

There will be assumed, by way of example, the case in which the crystalshave a solubility curve of the type C1.

A newly-formed fresh solution `which is slightly undersaturated has itscharacteristic point at S1, having an ordinate c1, corresponding to aconcentration which is as high as possible; its temperature is t1, whichis relatively high.

According to the invention, this fresh solution is introduced into thecentrifuge, with the following advantages:

Elimination of heat by the centrifuged crystals, and therefore coolingof the entering solution;

Heating of the outgoing centrifuged crystals, which facilitates theirsubsequent drying and economizes the heat necessary for this drying;

`Centrifuging of the crystals in the presence of the purest liquidphase, the entering solution being necessarily purer than the solutionin circuit, since the impurities are successively re-cycled into thiscircuit and therefore accumulate there;

Elimination by dissolving of the nuclei which would have a tendency tobe formed in an undesirable manner in the centrifuge.

The advantages are found in a symmetrical manner with respect to thevertical line tD, in the case in which the solubility curve of thecrystals is of the type shown by the curve C2.

F or the reasons given above, the under-saturated liquor conveyed by thepipe 62 axially through, but isolated from the suspension outlet conduit58 of the centrifuge attacks the nuclei first in tank 54 in preferenceto the crystals which are located in this conduit after having passedthrough the basket of the centrifuge.

However, in the case where the liquor circulating in this conduit doesnot have any crystals or only comprises an insucient number, the supplyof pre-formed crystals to the vessel 13 would be ensured, either byincreasing the flow taken by the valve 45 from the delivery of the pump40, or by connecting the said delivery to the inlet 70 through aregulating valve 76 interposed on a branch circuit 77 on the one hand,as shown in broken lines in *FIG. 1, and on the other hand through thefractionating means 65.

This fractionating means has the purpose of maintaining constant thenumber of crystals'contained in the crystallization unit and ofreplacing the number of crystals extracted by an equal number of brokencrystals introduced into this crystallization unit.

It should furthermore be noted that, in accordance with the invention,the fractionating means is operative in the liquid phase.

FIG. 6 relates, by way of example, to an installation with three stagesor eifects A, B and C. In this figure, the elements previously describedhave been given the same reference numbers, to which is added howeverthe letter A, B, or C corresponding to the effect or stage to which theybelong. Each effect A, B and C comprises an evaporation circuit 10A,10B, 10C respectively; in order to simplify the drawing, it has beenassumed that a single product is crystallized in the installation, andthere is therefore only a single centrifuge circuit 11.

The fresh solvent vapour coming in through the pipe 37 is directedinside the elements 21A of the exchanger 12A of the effect A or firsteffects; the secondary vapour collected by the cone 27A of thisexchanger 12A is directed inside the elements 21B of the exchanger 12Bof the effect B, or second effect; and then similarly, the tertiaryvapour collected by the cone 27B of the exchanger 12B is directed insidethe elements 21C of the exchanger 12C of the effect C, or third effect;finally, the fourth vapour collected by the cone 27C of the exchanger12C is directed over a condenser 80 connected by a conduit 31 to avacuum pump (not shown). This same conduit 81 also collects the vapourscondensed in the various exchangers.

'Ihe treated liquor circulates in the opposite direction. It passes at61 into the centrifuge 48', as previously, and then after being chargedwith the crystals passing through the basket of the centrifuge andpassing into the fractionating means 65, it is sent by the pump 40 intothe distribution pipes 25C of the exchanger 12C.

After collection by a pump C, it is delivered by this latter to thedistribution pipes 25B of the exchanger 12B, Finally, after a similarpassage into the exchanger 12A, it is collected by a pump 85A anddelivered by this latter to the hydro-cyclone 43.

The spent liquor passes out at 146 and can for example be conveyed to acooling circuit for the subsequent deposit of another solid.

FIGS. 7 to 1l relate to an alternative form of construction of the heatexchanger 12 according to the invention.

Following this alternative, the body 1.20 of this exchanger is as shownin FIGS. 7 and 8 horizontal and is provided laterally with rollers 121intended to roll on rails 122. This arrangement makes it possible tohave very easy access to the exchange elements 21 in case of need.

The body terminates in ange 123 intended for fixing it rigidly, forexample by bolting, to a cover 124 to which are connected the vapouroutlet 13.2 with a discharge nozzle or the like, and the evacuation pipe13-9.

The arrangement also includes steam inlet 142 and condensate outlet 143.

The distributor pipes 25 of the previous embodiment are replaced in thisalternative form by a unit 125 in the form of a comb (FIGS. 7-10).

This unit 125 is shown in FIGS. 9, 10A, 10B and ll to comprise an upperclosure plate 126 and a plurality of parallel channels 1,27. Eachchannel 127 is convergent horizontally between an inlet 1.28 at one endof unit 125 and an outlet 129 arranged at the other end thereof, but hasalways the same dimension in the vertical direction.

Each channel 127 is formed by two vertical Walls 130, 131, whichAgradually approach each otherand which are directed towards each otherby horizontal returns 133, 134 respectively, forming conjointly a slot135 of constant width.

The slots 135 of the unit 125 are engaged over the upper edges of theexchange elements 21 and substantially overlap these latter.

A unit of this -kind ensures a very uniform distribution and permits aconsiderable delivery of vapour. Any liquid which is delivered to unit125 and which does not leave via slots 135, simply exits via outlet 129,falls to the bottom of body 120, and is removed with the other liquid.

It will be understood that the heat exchanger described above mayequally serve as a cooler in the case especially where a crystallizationis desired and this crystallization necessitates a cooling action.

FIGS. 13 to 17 relate to an alternative form of construction of thisexchanger.

As previously, this latter comprises as shown in FIGS. 13 and 15 acylindrical body or casing 220` with a horizontal axis, providedlaterally with rollers 221 for moving on rails 222. 'Ihe body 220` isterminated by a flange 223 for fixing, for example by bolting, to acover 224.

In FIG. 13, the body 220 is shown removed from the cover 224 to adistance from this latter, in order to show the nest of tubes 225 of theexchange elements 226 which the body is intended to protect.

Each of the heat exchange elements 226 has, in a plane perpendicular tothe axis of body 120, a substantially rectangular contour (see FIGS. 14and l5) and in prole an undulating contour as shown in FIGS. 13 and 17.It is composed of two similar thin walls 227, 228, which are spaceduniformly apart by a distance D. Each of these walls has corrugations,the period, amplitude and number of which are chosen so that, takingaccount of its thickness, it is capable of resisting without permanentdeformation, the difference in pressures capable of existing on eachside. These walls 227, 228 are then simply welded to each other at theirperiphery without mutual intermediate supports.

At their upper portion, the walls 227, 2281 of an element 226 areprovided with a sharp edge 229, the purpose of which will becomeapparent below. This edge may be added, for example by welding.

The exchange elements 226 extend transversely with respect to thelongitudinal axis of the body 220, so that when the latter is withdrawnthe edges of elements 2.26 are on the outside. This arrangementfacilitates cleaning of these elements by a jet of water, and alsoprovides for the possible addition of supplementary elements at the endof those previously incorporated, with the corresponding addition of acylindrical portion to the body 2.20.

As indicated in a diagrammatic manner in FIGS. 14 and 15, the assemblyof the elements 226 permits the formation peripherally between them andthe body 220I of the chambers V1, V2, V3` and V4, the chamber V1 beingthe extreme left-hand chamber on the said figures and the chambers V2 toV4 being then spaced apart and distributed around elements 226 in theclockwise direction.

The exchange elements 226 are mounted to project in the same way as theteeth of a comb (see FIG. 16) from a common vertical distribution casing230i arranged inside the chamber V1 defined above. The internal volumeof this casing communicates with the internal space 231 of each element,In FIG. 16, the elements 226 are shown in a rectilinear manner, detachedfrom each other for the sake of clearness of the drawing. However, asshown in FIG. 17, these elements are preferably slightly reentrant ineach other.

The distribution casing `230 is provided with a supply conduit 232 whichpasses through the cover 224, and at the same time the elements 226 areconnected together at their lower portion by an evacuation conduit 233,which also passes through the cover 224, as shown in FIGS. 13 and 16.The assembly can easily be made dismantlable.

With the elements 226 is associated a distributor unit 235, mountedabove the units in the chamber V2, as defined above. This distributorunit, which is preferably but not necessarily of the same type as thatdescribed in French Patent No. 1,531,361, comprises a respectivetransverse discharge nozzle 236 (FIGS. 13 and 17) located verticallyabove the sharp edge 229 of each element 226.

This distribution unit 2315 which advantageously ensures a smoothprojection of the treated solution and not a spraying effect, is coupledto a supply pipe 237 which passes through the cover 224, preferably in aremovable manner.

This cover 224 is also traversed by a vapor removal conduit 2381 openinginto chamber V3 which is at right angles to the chamber V2, and by aconcentrate removal conduit 239 leading from chamber V4.

As previously stated, an exchanger of this kind may also serve as acrystallization body, whether this crystallization is effected bycooling or by evaporation.

In the following text it will be assumed that it is effected byevaporation.

The distribution unit 235, supplied from the pipe 237, causes the mothersolution to stream in thin dilms over the walls of the exchange elements226, the sharp edges of these latter ensuring a good distribution ofthis solution over each of their walls. The elements 226 are suppliedwith live steam by the pipe 232 and the distribution casing 230. Thesteam condensed at 231 in the elements 2126 is evacuated by the pipe233, while the solution which has streamed over the elements 226 iscollected in the chamber V4, from which it is evacuated by the pipe2-39. In contact with the elements 226, the solution treated becomesconcentrated under the most favorable conditions of micro-agitation,advantageously avoiding any excess heating. This micro-agitation is dueto the turbulent streaming of the solution over the elements 226 and isfacilitated by the corrugated profile of these latter, or moregenerally, by the changes in slope of the said profile.

With regard to the vapour liberated by the solution treated, this iscollected in the chamber V3 and evacuated by the tube 238, for exampletowards a condenser or a. vacuum ejector.

There should be noted the particularly rational use of the internalspace of an exchanger of this kind, this use being made possible by thearrangement according to the invention, of a nest of exchange elementsplaced trans versely in the interior of a cylindrical body.

According to an arrangement which is not shown in FIG. 17, the mostupstream nozzle 236, that is to say the nozzle 236 which is nearest tothe co'ver 224, is preferably wider than the others so as to permit thepassage of all the crystals which may travel into the pipe 237, thusavoiding a possible obstruction of the other nozzles.

In accordance with the alternative form of construction showndiagrammatically in FIG. 18, the exchange elements 226 may equally wellhave a zig-zag profile.

Following an arrangement which is not shown in the drawings, spacingmembers are preferably provided at the overhanging extremities of theelements 226. These spacing members which are preferably adjustable,have a double purpose: on the one hand to compensate for the effects ofthe differential expansion of the two longitudinal walls of the casing230, and on the other hand to regulate the positions of the sharp edges229 of the elements 226 in the axes of the corresponding nozzles 236 ofthe distribution unit 235.

FIG. 19 relates to an alternative form, in which the sharp edge 229 ofan element 226 is formed by an extension of one of the walls 227, 228 ofthis element to form a tongue, this extension being preferablydeformable with respect to its connection or coupling line to the otherwall. The spacing members referred to above enable the regulation bydeformation of the position of this extension with respect to theassociated nozzle 236 (not shown in the drawing), as indicated in brokenlines.

In the foregoing description, it has been assumed that thecrystallization concerned was effected by evaporation. -ln the casewhere this crystallization is effected by cooling, that 1s to say in thecase where the heat exchanger accordmg to the invention is utilized as acooler, the refrigerating fluid necessary may be introduced through thepipe 232 and passes out heated through the pipe 233, although it ispreferable from the thermal point of view to introduce it at 233 and toevacuate it at 232.

For the reasons explained above, the introduction of the fresh solutioninto the centrifuge of the installation according to the invention has anumber of advantages.

It will be understood that in the case where the above advantages arenot sought for automatically, the fresh solution may be introduced at apoint other than into the centrifuge,

This is especially the case when special arrangements are made inaddition, to avoid the formation of nuclei in the centrifuge.

There will now be described, with reference to FIGS. 20 and 21, acentrifuge 260 provided in accordance with the invention witharrangements adopted precisely for that purpose.

The perforated basket 26'1 of this centrifuge is carried by a skirt 262keyed for rotation on a driving shaft 263. In a manner known per se,there is associated therewith one or a plurality of helical Scrapers 264carried by a support 265, and this support is keyed for rotation with ashaft 266 mounted in the interior of the shaft 263 and coaxialtherewith. The shaft 266 may be fixed or it may rotate at the same speedas the basket 261 or it may rotate at a different speed by braking or bya motor.

The crystals to be centrifuged are introduced into the mouth 267 of thebasket 261, and, after sliding along the internal wall of this backetunder the control of the v11 scraper or scrapers 264, they are evacuatedat 268.

This arrangement is well known.

It has however the disadvantage that any undesired ventilation producedthrough the sieve by the relative rotary movements of the basket 261 andthe scraper or scrapers 264, is favourable to the formation of nucleiand causes blocking-up of the basket 261 and also causes the crystals toset in a mass during the course of centrifuging.

According -to the invention, the basket 261 is extended laterally by aplate 270 and is capped by a bell 271.

Between this bell 271 and the basket 261 there is only left a smallspace 275 which opens to the exterior through an annular slot 276 at theextremity of the plate 270.

The dimensions of this slot are adjusted so that its flow-rate is atmost equal to the theoretical liquid flowrate of the centrifuge.

By this means, the space 275 is lled with liquid and any circulation ofair through it is impossible, which eliminates the drawbacks referred toabove.

In the embodiment shown in FIG. 2l, the outlet of liquid is effectedalong a ring, as shown diagrammatically at 277.

In an alternative form shown diagrammatically in FIG. 22, the aboveoutlet slot 276 is replaced by a plurality of peripheral nozzles 278oriented tangentially and uniformly spaced apart around the periphery.

These nozzles make it possible to recover from the liquid a part of `theenergy of rotation which has been given to them by the basket 261 andtherefore economically reduces the energy necessary for the rotation ofthis basket 261.

It Awill of course be understood that the present invention is notlimited to the forms of construction described above, but includes allits alternative forms of execution, especially as regards the plancontour of the exchange elements which could equally well be curvilineror zig-zag.

What I claim is:

1. An installation for the continuous evaporation of any solvent and forthe continuous concentration of at least one substance in solution insaid solvent, of the kind comprising an indirect heat exchanger throughwhich circulate, on the one hand, the solution to be treated and, on theother hand, a heat exchange uid, in which said heat exchanger comprisesa housing body, a plurality of similar exchange elements arranged inparallel and spaced apart from each other inside said body, each saidelement being closed and composed of two substantially vertical thinwalls disposed at a short distance from each other, a primary heatingvapor intake adapted to introduce said exchange fluid between saidWalls, and a secondary solution intake causing said solution to streamover said walls, said secondary intake comprising as many substantiallyhorizontal elongate discharge outlet nozzles as there are heat exchangeelements, and each of said nozzles being arranged directly above theupper edge of a respective one of said exchange elements, said secondaryintake being constituted by a unit having the shape of a comb andcomprising a plurality of elongate channels converging in theirlongitudinal direction and longitudinally slit at their lower portionsto provide said nozzles, said heat exchange elements being embraced bythe nozzles formed in said channels over the associated exchangeelements.

2. An installation as claimed in claim 1, in which said heat-exchangerserves at the same time as a heater and as an evaporator device.

3. An installation as claimed in claim 1, in which the walls of saidexchange elements are provided with transverse stiifening bosses.

4. An installation as claimed in claim 1, in which the walls of a saidexchange element have a profile presenting changes of slope.

5. An installation as claimed in claim 1, in which each of said exchangeelements is provided with a tapering edge 12 facing the correspondingoutlet nozzle of the intake for said solution.

6. An installation as claimed in claim 5, in which said tapered edge isconstituted by an extension of one of the Walls of said exchangeelement.

7. An installation as claimed in claim 6, in which said wall extensionis deformable with respect to its line of coupling to the other wall ofsaid exchange element.

8. An installation for the continuous evaporation of any solvent and forthe continuous concentration of at least one substance in solution insaid solvent, of the kind comprising an indirect heat exchanger throughwhich circulate, on the one hand, the solution to be treated, and on theother hand, a heat-exchange fluid, in which said heat exchangercomprises a housing body in the form of a circular cylinder having asubstantially horizontal axis, a plurality of similar, vertical exchangeelements arranged in parallel, spaced apart from each other inside saidbody, and disposed transversely with respect to the axis of said body,each said element being closed and composed of two thin substantiallyvertical walls disposed at a short distance from each other, a primaryheating vapor intake adapted to introduce said exchange uid between saidwalls, and a secondary solution intake causing said solution to streamover said walls, said secondary intake comprising as many outlet nozzlesas there are exchange elements, and each of said nozzles being arrangeddirectly above the upper edge of one of said exchange elements.

`9. An installation as claimed in claim 8, in which said exchangeelements have a rectangular outline and are adapted to form fouradjoining peripheral chambers with the cylindrical body in which theyare contained, one said chamber comprising the primary intake for saidexchange Huid, a second chamber comprising the secondary intake for saidsolution, a third chamber comprising an outlet for the solution vapourformed, and a fourth chamber comprising an outlet for the remainder ofthe nonevaporated solution, a further outlet being provided for theevacuation of the fluid condensed in said exchange elements.

110. An installation as claimed in claim 8, in which said exchangeelements are mounted in a cantilever position on a distribution casing,the internal space of said casing being adapted to communicate, on theone hand, with the internal space of each of said elements and, on theother hand, with the primary intake provided for said exchange fluid.

11. An installation for the continuous evaporation of any solvent andfor the continuous concentration of at least one substance in solutionin said solvent, of the kind comprising an indirect heat exchangerthrough which circulate, on the one hand, the solution to be treatedand, on the other hand, a heat-exchange uid, in which said heatexchanger comprises a housing body, a plurality of similar exchangeelements arranged in parallel and spaced apart from each other insidesaid body, each said element being closed and composed of twosubstantially vertical thin walls disposed at a short distance from eachother, a primary heating vapor intake adapted to introduce said exchangefluid between said walls, and a secondary solution intake causing saidsolution to stream over said walls, said secondary intake comprising adistributor unit having its bottom provided with as many elongatedischarge outlet nozzles as there are exchange elements, each of saidnozzles being arranged directly above and parallel to the upper edge ofa respective one of said exchange elements, said distributor conveyingsolution in a direction transverse to said nozzles, and that one of saidsecondary solution nozzles which is in the farthest upstream positionwith respect to the direction of solution flow being wider than thesucceeding nozzles.

12. An installation as claimed in claim 11, in which said secondaryintake of the exchanger is constituted by a plurality of tubes each slitalong a generator line and having the slot thus formed embracing theupper edge of the associated exchange element.

13'. An installation as claimed in claim 12, in which the axis of eachof said tubes is inclined with respect to the general direction of thesaid upper edge of the associated exchange element.

14. An installation for the continuous evaporation of any solvent andfor the continuous concentration of at least one substance in solutionin said solvent and the extraction of crystals of said substance, of the`kind comprising an indirect heat exchanger through which circulate, onthe one hand, the solution to be treated and, on the other hand, aheat-exchange fluid, in which said heat exchanger comprises a housingbody, a plurality of similar exchange elements arranged in parallel andspaced apart from each other inside said body, each said element beingcomposed of two substantially vertical thin walls disposed at a shortdistance from each other, a primary heating vapor intake adapted tointroduce said exchange iluid between said walls, and a secondarysolution intake causing said solution to stream over said Walls, tocause part of said solution to be evaporated by thermal exchange withsaid exchange fluid and the remainder of said uid to remain in itsliquid state and to fall to the bottom of the interior of said bodyafter traversing said walls, said secondary intake comprising as manyelongate discharge outlet nozzles as there are exchange elements, andeach of said nozzles being arranged directly above the upper edge of oneof said exchange elements, said installation further comprising: acentrifugal separation device for circulating a liquid and having a rstinlet in communication with the bottom of the interior of said body forreceiving the liquid thereat and an outlet in communication with saidsecondary intake for delivering solution thereto, said heat exchangerand said separation device forming an evaporation circuit, saidcentrifugal separation device further having a second inlet; meansconnected to said second inlet for delivering pre-formed crystals ofsaid substance to said centrifugal separation device; and a centrifugalliquid-solid separation circuit connected in parallel with saidevaporation circuit, said separation circuit comprising a liquid-solidseparating centrifuge having a centrifuging basket and having a rstinlet connected to receive from said centrifugal separation device, viaa pump, a crystal bearing concentrated solution which is delivered tothe interior of said basket, and a second inlet connected to receive asupply of undersaturated fresh solution delivered to the exterior ofsaid basket.

15. An installation as claimed in claim 14, in which said centrifuge isfed by a hydro-cyclone.

16. An installation as claimed in claim 14, and further comprising aplurality of evaporation circuits arranged in cascade.

17. An installation as claimed in claim 14, in which said basket of saidcentrifuge rotates in a chamber connected by a delivery pipe to saidsecond inlet of said separation device of said evaporation circuit.

18. An installation as claimed in claim 17, in which said delivery pipeencloses a counter-110W intake pipe for undersaturated solution, openinginto said chamber.

19. An installation as claimed in claim 14, and further comprisingcrystal-fractionating means provided at any point of sai dinstallation,said means being constituted by a mixer, grinder or the like.

20. An installation as claimed in claim 19, in which said fractionatingmeans operate in the liquid phase.

211. An installation for the continuous evaporation of any solvent andfor the continuous concentration of at least one substance in solutionin said solvent and the extraction of crystals of said substance, of thekind comprising an indirect heat exchanger through which circulate, onthe one hand, the solution to be treated and, on the other hand, aheat-exchange fluid, in which said heat exchanger comprises a housingbody, a plurality of similar exchange elements arranged in parallel andspaced apart from each other inside said body, each said element beingcomposed of two substantially vertical thin Walls disposed at a shortdistance from each other, a primary heating vapor intake adapted tointroduce said exchange fluid between said Walls, and a secondarysolution intake causing said solution to stream over said walls, tocause part of said solution to be evaporated by thermal exchange withsaid exchange fluid and the remainder of said Huid to remain in itsliquid state and to fall to the bottom of the interior of said bodyafter traversing said walls, said secondary intake comprising as manyelongate discharge outlet nozzles as there are exchange elements, andeach of said nozzles being arranged directly above the upper edge of oneof said exchange elements, said installation further comprising: acentrifugal separation device for circulating a liquid and having afirst inlet in communication with the bottom of the interior of saidbody for receiving the liquid thereat and an outlet in communicationwith said secondary intake for delivering solution thereto, said heatexchanger and said centrifugal separation device forming an evaporationcircuit, said centrifugal separation device forming an evaporationcircuit, said centrifugal separation device further having a secondinlet; means connected to said second inlet for delivering pre-formedcrystals of said substance to said centrifugal separation device; and acentrifugal liquid-solid separation circuit connected in parallel withsaid evaporation circuit, said centrifugal separation circuit comprisinga centrifuge having a perforate basket capped by a bell spaced a smalldistance from said basket, the space between said basket and said bellbeing provided with liquid discharge openings dimensioned to permit amaximum rate of flow which is equal to the theoretical liquid outflowrate of said centrifuge. 22. An installation as claimed in claim 21, inwhich said liquid discharge openings are formed as nozzles disposedtangentially to the basket periphery and perpendicularly skew to theaxis of rotation of said basket.

References Cited UNITED STATES PATENTS 743,352 11/1903 Trump 159-27 A X1,501,646 7/1924 Brown 159-1218 C 2,194,014 3/194() Ehrman 1165--1152,343,886 3/1944 Cornell, Ir 159--3 X 2,739,044 3/1956 Ashley et al23,-302 2,805,557 9/1957 Hilger 165-115 X 3,351,119 11/1967 Rosenblad159-13 B 3,371,709 3/11968 Rosenblad 159-28 X FOREIGN PATENTS 1,003,4793/1952 France.

NORMAN YUDKOFF, Primary Examiner J. SOFER, Assistant Examiner U.S. Cl.X.R.

